An abrasive substance has been included in conventional dentifrice compositions in order to remove various deposits, including pellicle film, from the surface of teeth. Pellicle film is tightly adherent and often contains brown or yellow pigments which impart an unsightly appearance to the teeth. While cleaning is important, the abrasive should not be so aggressive so as to damage the teeth. Ideally, an effective dentifrice abrasive material maximizes pellicle film removal while causing minimal abrasion and damage to the hard tooth tissues. Consequently, among other things, the performance of the dentifrice is highly sensitive to the extent of abrasion caused by the abrasive ingredient. Conventionally, the abrasive cleaning material has been introduced in flowable dry powder form to dentifrice compositions, or via redispersions of flowable dry powder forms of the polishing agent prepared before or at the time of formulating the dentifrice. Also, and more recently, slurry forms of such abrasives have been provided to facilitate storage, transport, and introduction within target dentifrice formulations.
Synthetic low-structure silicas have been utilized for such a purpose due to the effectiveness such materials provide as abrasives, as well as low toxicity characteristics and compatibility with other dentifrice components, such as sodium fluoride, as one example. When preparing synthetic silicas, the objective is to obtain silicas which provide maximal cleaning with minimal impact to the hard tooth surfaces. Dental researchers are continually concerned with identifying abrasive materials that meet such objectives.
Synthetic silicas (of higher structure) have also been utilized as thickening agents for dentifrices and other like paste materials in order to supplement and modify the rheological properties for improved control, such as viscosity build, stand up, brush sag, and the like. For toothpaste formulations, for example, there is a need to provide a stable paste that can meet a number of consumer requirements, including, and without limitation, the ability to be transferred out of a container (such as a tube) via pressure (i.e., squeezing of the tube) as a dimensionally stable paste and to return to its previous state upon removal of such pressure, the ability to be transferred in such a manner to a brushhead easily and without flow out of the tube during and after such transference, the propensity to remain dimensionally stable on the brush prior to use and when applied to target teeth prior to brushing, and the exhibiting of proper mouthfeel for aesthetic purposes, at least, for the benefit of the user.
Generally, dentifrices comprise a majority of a humectant (such as sorbitol, glycerin, polyethylene glycol, and the like) in order to permit proper contact with target dental subjects, an abrasive (such as precipitated silica) for proper cleaning and abrading of the subject teeth, water, and other active components (such as fluoride-based compounds for anticaries benefits). The ability to impart proper rheological benefits to such a dentifrice is accorded through the proper selection and utilization of thickening agents (such as hydrated silicas, hydrocolloids, gums, and the like) to form a proper network of support to properly contain such important humectant, abrasive, and anticaries ingredients. It is thus evident that formulating proper dentifrice compositions can be rather complex, both from a compounding standpoint as well as the number, amount, and type of components present within such formulations. As a result, although it is not a high priority within the dentifrice industry, the ability to reduce the number of such components, or attempt to provide certain components that meet at least two of these needed properties could potentially reduce formulation complexity, not to mention potentially reducing the overall manufacturing costs.
A number of water-insoluble, abrasive polishing agents have been used or described for dentifrice compositions. These abrasive polishing agents include natural and synthetic abrasive particulate materials. The generally known synthetic abrasive polishing agents include amorphous precipitated silicas and silica gels and precipitated calcium carbonate (PCC). Other abrasive polishing agents for dentifrices have included chalk, magnesium carbonate, dicalcium phosphate and its dihydrate forms, calcium pyrophosphate, zirconium silicate, potassium metaphosphate, magnesium orthophosphate, tricalcium phosphate, perlite, and the like.
Synthetically-produced precipitated low-structure silicas, in particular, have been used as abrasive components in dentifrice formulations due to their cleaning ability, relative safeness, and compatibility with typical dentifrice ingredients, such as humectants, thickening agents, flavoring agents, anticaries agents, and so forth. As known, synthetic precipitated silicas generally are produced by the destabilization and precipitation of amorphous silica from soluble alkaline silicate by the addition of a mineral acid and/or acid gases under conditions in which primary particles initially formed tend to associate with each other to form a plurality of aggregates (i.e., discrete clusters of primary particles), but without agglomeration into a three-dimensional gel structure. The resulting precipitate is separated from the aqueous fraction of the reaction mixture by filtering, washing, and drying procedures, and then the dried product is mechanically comminuted in order to provide a suitable particle size and size distribution.
The silica drying procedures are conventionally accomplished using spray drying, nozzle drying (e.g., tower or fountain), wheel drying, flash drying, rotary wheel drying, oven/fluid bed drying, and the like.
As it is, such conventional abrasive materials suffer to a certain extent from limitations associated with maximizing cleaning and minimizing dentin abrasion. The ability to optimize such characteristics in the past has been limited generally to controlling the structures of the individual components utilized for such purposes. Examples of modifications in precipitated silica structures for such dentifrice purposes are described in the art within such publications as U.S. Pat. Nos. 3,967,563, 3,988,162, 4,420,312, and 4,122,161 to Wason, U.S. Pat. Nos. 4,992,251 and 5,035,879 to Aldcroft et al., U.S. Pat. No. 5,098,695 to Newton et al., and U.S. Pat. Nos. 5,891,421 and 5,419,888 to McGill et al. Modifications in silica gels have also been described within such publications as U.S. Pat. No. 5,647,903 to McGill et al., U.S. Pat. No. 4,303,641, to DeWolf, II et al., U.S. Pat. No. 4,153,680, to Seybert, and U.S. Pat. No. 3,538,230, to Pader et al. Such disclosures teach improvement in such silica materials in order to impart increased pellicle film cleaning capacity and reductions in dentin abrasion levels for dentifrice benefits. However, these typical improvements lack the ability to deliver preferred property levels that accord a dentifrice producer the ability incorporate such an individual material in different amounts with other like components in order to effectuate different resultant levels of such cleaning and abrasion characteristics. To compensate for such limitations, attempts have been undertaken to provide various combinations of silicas to permit targeting of different levels. Such silica combinations involving compositions of differing particle sizes and specific surface areas are disclosed in U.S. Pat. No. 3,577,521. to Karlheinz Scheller et al., U.S. Pat. No. 4,618,488 to Macyarea et al., U.S. Pat. No. 5,124,143 to Muhlemann, and U.S. Pat. No. 4,632,826 to Ploger et al. Such resultant dentifrices, however, fail to provide desired levels of abrasion and high pellicle cleaning simultaneously.
Another attempt has been made to provide physical mixtures of precipitated silicas of certain structures with silica gels, notably within U.S. Pat. No. 5,658,553 to Rice. It is generally accepted that silica gels exhibit edges, and thus theoretically exhibit the ability to abrade surfaces to a greater degree, than precipitated silicas, even low structured types. Thus, the blend of such materials together within this patent provided, at that time, an improvement in terms of controlled but higher levels of abrasiveness coupled with greater pellicle film cleaning ability than precipitated silicas alone. In such a disclosure, it is shown that separately produced and co-incorporated silica gels and precipitated silicas can permit increased PCR and RDA levels but with apparently greater control for lower abrasive characteristics than for previously provided silicas exhibiting very high PCR results. Unfortunately, although these results are certainly a step in the right direction, there is still a largely unfulfilled need to provide a silica-based dental abrasive that exhibits sufficiently high pellicle film cleaning properties with simultaneously lower radioactive dentin abrasive characteristics such that film removal can be accomplished without deleterious dentin destruction. In effect, the need is for a safer abrasive that exhibits a significantly higher PCR level versus RDA level than has previously been provided within the dental silica industry. Again, the Rice patent is merely a start toward desirable abrasive characteristics. Furthermore, the requirement to produce these separate gel and precipitate materials and meter them out for proper target levels of such characteristics adds costs and process steps to the manufacturing procedure. A manner of providing the benefits of such combinations, but to a very high level of pellicle film cleaning and at a relatively low to moderate degree of dentin abrasion, with simultaneous facilitation of incorporation within dentifrice formulation are thus unavailable to the industry at this time.
There is always a desire to limit the number of additives required for purchase, storage and introduction within dentifrice formulations. As such, the ability to provide simultaneous thickening and abrasive characteristics to avoid the addition of multiple components for such properties is an unmet need within the industry.